Electric power is essential to a modern industrial plant or ship's functional effectiveness. Electric power steers the ship, operates the ship's rudder hydraulic system, sensitive navigation systems, dynamic positioning systems, runs auxiliary systems for cooking and cleaning and provides light and power to interior systems. An industrial plant or ship without electric power is useless for its operational mission or purpose. The primary power distribution voltage, phase, and frequency used on many U.S. and international vessels are three-phase 50 or 60 Hz at 450-600 Volts AC. Secondary voltage, phase, and frequency are 120-240 Volts, single or three-phase, 50 or 60 Hz. The secondary voltage is derived from the primary voltage system through transformer banks and circuit breakers. Lighting distribution systems are 120-240 V, single or three-phase, 50 or 60 Hz and are supplied from the primary power circuits to transformer banks.